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Deepwater Sedimentary Processes and Systems in Deepwater Basin Margins


Deepwater sedimentary systems are different from most other sedimentary systems because their deposits are dominated by events representing relatively short time periods. In most other sedimentary environments, the deposits record longer time intervals. Across small areas, the relative roles of external factors may vary significantly, and it is of utmost importance to analyze each system independently.

Depositional systems in deepwater basin margins can be classified on the basis of grain size and feeder system into 12 classes: mud-rich, mud/sand-rich, sand-rich, and gravel-rich “point-source submarine fans;” mud-rich, mud/sand-rich, sand-rich, and gravel-rich “multiple-source submarine ramps;” and mud-rich, mud/sand-rich, sandrich, and gravel-rich “linear-source slope aprons.” The size and stability of channels and the organization of the depositional sequences decreases toward a linear source as does the length:width ratio of the system. As grain size increases, so does slope gradient, impersistence of channel systems, and tendency for channels to migrate. As grain size diminishes, there is an increase in the size of the source area, the size of the depositional system, the downcurrent length, the persistence and size of flows, fan channels, channellevee systems, and in the tendency to meander and for major slumps and sheet sands to reach the lower fan and basin plain. The exact positioning of any one depositional system within the scheme cannot always be precise, and the position may be altered by changes in tectonics, climate, supply, and sea level.